Why does oxygen and hydrogen burn, while the combination of the two puts out fires?

Why does sodium blow up in water, but sodium and chloride together makes my food taste better? If you really want a book about chemistry basics, I could try to find one to send to you.

In simple terms, water is much more stable than the uncombined hydrogen and oxygen. Chemical reactions go from less stable to more stable configurations.

Water Is naturally broken down as part of the photosynthesis process, which requires energy from the sun. Animals and plants reverse the process in respiration, using the energy that is released.

photosynthesis:
6CO2 + 6H2O + energy ———> C6H12O6 + 6O2

respiration:
C6H12O6 + 6O2 ———> 6CO2 + 6H2O + energy

The same reason you can not burn ash.

^ @ragingloli ‘s got it.
I was thinking along the same lines. Water is “already burned” hydrogen. It’s done. (ignore thermonuclear reactions).
Wood reacts with oxygen and burns. The stuff that’s left, CO2, H2O, and ash are finished reacting. They’re done. Toss any of them on a fire and they put it out.

As @LuckyGuy said, it is “already burned”, done. H2 and O2 reacted and released a lot of energy. Trying to break it back apart will require just as much energy put back in. Most fires do not have that much energy, so would have to deal with H2O and its watery properties (which will then put them out).

Water istill has the potential to burn through the process of electrolysis.

That is actually the reverse of burning.